High Density Wafer Bumping with Solder Paste

摘要

Wafer bumping with solder paste is projected to double each year through 2006. Although pitches less than 150 microns have been bumped with solder paste, the majority of applications using stencil printing of fine particle solder pastes are greater than 200 micron pitch. In order to get an adequate reflowed bump height overprinting the UBM is commonplace. Tight pitches combined with large apertures pushes both stencil fabrication and paste slump properties to their respective technology limits. This paper reports the highest bump height to pitch ratio possible with today's solder paste and stencil technologies. Bump heights are quantified for numerous aperture area/pitch combinations via non contact measurement methods for pitches in the 150μ to 250μ range using full array designs. Bump statistics using type 5 and type 6 powder Sn/Pb and Sn/Ag/Cu lead free water clean pastes are compared and contrasted.